Fish Larvae Research Articles

Effects of carotenoid supplementation on colour, growth and physiological function of the endemic dwarf chameleon fish (Badis badis).

The global ornamental fish trade is expanding in response to increased demand for indigenous fish on the global market, while exogenous carotenoids can improve colouration. The 60-day trial investigated the effect of carotenoid supplementation, via Artemia, on colouration, growth and immunophysiology of Badis badis (dwarf chameleon fish). Carotenoid was enriched at 40 ppm (T1), 80 ppm (T2) and 120 ppm (T3) and compared with controls, C1 (unenriched) and C2 (oil-enriched). Fish larvae (average weight 0.12 g) were fed enriched-unenriched Artemia in triplicates (5 × 3) in aquarium tanks (15 L). C1 and T2 had better skin colour (lightness and whiteness) in the posterolateral and caudal fins respectively. The value of redness (a*) in the anterolateral region was higher in T2 and T3 (p < 0.05). The anterolateral red index was higher (p < 0.05) in T2 and T3, whereas in the posterolateral and caudal fins, T1 and T2 were higher (p < 0.05). Compared to C1 and C2, the hue angle in carotenoid groups was found to be low (p < 0.05). No significant change in the growth performance was noticed (p > 0.05). Immune scores such as lysozyme and alkaline protease were highest in T3 (p < 0.05), whereas protease activity was highest in T2 (80 ppm). Stress biomarkers, viz., superoxide dismutase, catalase and malondialdehyde were low in groups fed enriched Artemia (p < 0.05). The integrated biomarker response means and star plot area were lower in the enriched groups (T1-T3), while T2 was the lowest. Overall findings reveal that dietary carotenoid improves the colouration and immune status, but fail to promote growth. Furthermore, 80 ppm enrichment dose improves the overall performance. The findings can help fish keepers improve fish colour and health status through carotenoid supplementation.

Importance of Infusoria as Live Feed for Fish Larvae and its Cultivation Techniques

Importance of Infusoria as Live Feed for Fish Larvae and its Cultivation Techniques

Body condition variation in a riverine piscivore: have small non-native cyprinids benefited an endangered fish?

Relations between annual abundance of three introduced fishes and body condition of an endangered piscivore, Colorado pikeminnow Ptychocheilus lucius, in the upper Colorado River were assessed to aid prioritization of non-native fish control efforts. Relative condition (Kn: mass at a given length) was monitored during spring, 1991–2013. Positive and significant relations were found between annual mean Kn and backwater densities of two common non-native, small-bodied, cyprinid species in downstream reaches of the 293 km study area. High mean Kn in spring followed years when fall densities of fathead minnow Pimephales promelas and red shiner Cyprinella lutrensis were high. No such relation was found with a third species, sand shiner Notropis stramineus. These three species have dominated zero-velocity habitats since their introduction in the 1960s. No relation was found between mean Kn prior to spawning and subsequent abundance of Colorado pikeminnow young-of-the-year (YOY) 3 months post spawning, suggesting mean Kn was not a driver of fall YOY abundance. Based on predatory interactions with larval native fishes documented in the literature, red shiners were deemed detrimental to Colorado pikeminnow despite their food value. Sand shiners appeared benign: non-predatory and less important as food. Fathead minnows, however, might be beneficial. They appear non-predatory on fish larvae while providing an important food source for various Colorado pikeminnow life stages. Managers need to weigh these benefits when considering control efforts.

Morphological and Trophic Features of the Invasive Babka gymnotrachelus (Gobiidae) in the Plain and Mountainous Ecosystems of the Dniester Basin: Spatiotemporal Expansion and Possible Threats to Native Fishes

Over the last few years, the racer goby B. gymnotrachelus quickly expanded in the mountainous rivers of the Dniester basin at aheight of 300 m a.s.l. and above. The occurrence frequency of the racer goby in fish communities in the mountainous rivers of the Carpathian ecoregion remains low (up to 20%), as compared with the plain rivers, where the species occurs in 70–100% of cases. The major prey groups in its diet in both plain and mountainous were Chironomidae, Diptera, and Crustacea. Chironomidae formed the maximal portion (35% at an occurrence frequency of 72.5%), and Trichoptera formed 18%at an occurrence frequency of 41%, whereas fish larvae were absent in their diet in mountainous rivers. The peculiar environmental conditions of mountainous rivers caused the adaptive modifications of the morphological features of the racer goby at the subpopulation level, which compriseda decrease inthe specimens’ size in rivers with a flow velocity of above 1.5 m/s and rivers with pebble contentsof above 50%in the bottom sediments.The modifications showed an increase inbody streamlining as an adaptation to flow velocity and turbulence and the stony substrate of the river’s bottom. Thus, the morphological adaptation of B. gymnotrachelus to the conditions of the mountainous rivers is in progress, and the formationof astable population in these rivers can be expected. In contrast, the native fish species’ resilience in the face of newcomers is still high, and this is because their alevins are not food for invaders.

Leukolectin is expressed in lectophages, a distinct population of zebrafish embryonic macrophages

Leukolectins (LL) belong to the tectonin-family of proteins, with functions in innate immunity. Fish larvae compensating for loss of maternal chorionic protection post-hatching, provide a model-system for studying how lectins contribute to immunity. Atlantic salmon (Ssal) LL-proteins function after secretion in mucus from dermal lectocytes, as this mucus envelops embryos and larvae. The Ssalll-gene possesses multiple putative binding sites for diverse transcription-factors, suggestive of LL-functions in non-epithelial cells. Since zebrafish (zF) perivitelline fluid (PVF) contains LL-proteins, this study aims to characterize zF-leukolectins, their cellular origin, expression and gene structure. Extracts of (10 hpf) zF-embryos contained LL-proteins, and whole mount immuno-histochemistry revealed dispersed LL-positive cells including zF-lectocytes, accounting for exocrine LL-secretion by embryos. Lectocytes are lcp1-negative, but other zF-cells co-expressed LL-proteins and lcp1-transcripts, which (at this stage) identified such non-lectocytes as early macrophages (termed lectophages). In sections, LL-expression characterized large macrophage-progenitors and smaller colonizing macrophages. RT- and RACE-PCR yielded zF-LLcDNA including parts of untranslated regions. ORF encoded 255 AAs including (19 AA) signal peptide. Processing of a primary LL-transcript to (∼1.300 nt) LL-mRNA was suggested by Northern blots. Most zebrafish-egg lectins (zFELs) possess four TECPR-domains, while five TECPR-domains were predicted for zF-LL. Minor sequence variations suggested nearly identical zF-LL isoforms. Alignment of zFEL-proteins predicted a zFEL-tree with a separate leukolectin-branch. LL-amplification using zF-DNA, revealed five exons and four introns. Predicted structures of zF- and Ssal-leukolectins showed strong structural conservation (92% sequence-identity) with shorter zF-introns 2&4, but identical introns 1&3. Non-lectocytic LL-functions were investigated further by dual in situ hybridization, revealing that only some embryonic lcp1-expressing cells in early zF-embryos co-expressed LL-transcripts. Macrophages from erythro-myeloid progenitor (EMP) are known to colonize zebrafish tissues as resident macrophages (TRM), e.g. nervous system (CNS) and epiderm. Unlike Ssal-larvae relying on yolk for months, zF-larvae switch within days to nutrition from the digestive-tract, necessitating additional immuno-protection possibly from TRMs. EMP also gives rise to microglia, the TRM of CNS. The neural tube of zF-embryos exhibited numerous small, LL-positive cells, presumably stemming from lectophage-progenitors. Functions of these LL-positive embryonic microglia (lectoglia) appear more relevant for tissue remodelling than for pathogenic threats. Lectoglia sustaining CNS-neurons suggests physiological LL-roles relevant for adult health and disease. The data focus the need for resolving whether lectophages represent an unrecognized myelogenic lineage, or whether instead, LL-expression occurs in a subpopulation of the early macrophage-lineage.

Dopaminergic and serotoninergic neurotoxicity of lanthanide phosphate (TbPO4) in developing zebrafish

Rare earth elements (REEs) are exploited for global use in manufacturing. Such activities result in their release into the environment and the transformation into more stable phosphate deposition. The objective of this study was to evaluate molecular and behavioral changes of zebrafish exposed to the synthesized terbium phosphate (TbPO4) at concentrations of 10, 20, and 50 mg/L and to determine its potential for neurotoxicity. Metabolomics related to neurotransmitters, and assessment of transcripts and proteins were conducted to uncover the molecular mechanisms underlying TbPO4 with emphasis on neurotransmitter systems. Exposure to 20 mg/L TbPO4 induced larval hyperactivity and perturbed the cholinergic system in zebrafish. Based on metabolomics related to neurotransmitters, dopamine (DA), serotonin (5-HT), and many of their precursors and metabolites were decreased in abundance by TbPO4. In addition, the expression levels of transcripts related to the synthesis, transport, receptor binding, and metabolism of DA and 5-HT were analyzed at the mRNA and protein levels. Transcript and protein levels for tyrosine hydroxylase (TH), the rate-limiting enzyme for DA synthesis, were down-regulated in larval fish. Monoamine oxidase (MAO), an enzyme that catabolizes monoamines DA and 5-HT, was also reduced in mRNA abundance. We hypothesize that DA synthesis and monoamine metabolism are associated with behavioral alterations. This study elucidates putative mechanisms and exposure risks to wildlife and humans by characterizing phosphatic REE-induced neurotoxicity in developing zebrafish.

New species of Monomitopus (Ophidiidae) from Hawaii, with the description of a larval coiling behavior.

In 1985, Carter and Cohen noted that there are several yet-to-be described species of Monomitopus (Ophidiidae), including one from Hawaii. Recently, blackwater divers collected a larval fish off Kona, Hawaii, similar to the previously described larvae of M. kumae, but DNA sequence data from the larva does not match any of the six previously sequenced species within the genus. Within the Smithsonian Institutions National Museum of Natural History Ichthyology Collection, we find a single unidentified adult specimen of Monomitopus collected North of Maui, Hawaii in 1972 whose fin-ray and vertebral/myomere counts overlap those of the larval specimen. We describe this new Hawaiian species of Monomitopus based on larval and adult characters. Additionally, blackwater photographs of several species of Monomitopus show the larvae coiled into a tight ball, a novel behavior to be observed in cusk-eels. We describe this behavior, highlighting the importance of blackwater photography in advancing our understanding of marine larval fish biology.

Stable isotope values and trophic analysis of invasive three-spined stickleback in Upper Lake Constance points to significant piscivory

The three-spined stickleback Gasterosteus aculeatus was introduced into Lake Constance in the 1940s and occupied a limited range until late 2012. Since then the species has expanded from a solely littoral habitat in Upper Lake Constance, but now makes seasonal migrations into the pelagic zone. This behavioral change has been accompanied by a drastic increase in stickleback abundance. In order to integrate information about feeding of sticklebacks in Upper Lake Constance over two consecutive years, stomach content analysis was combined with seasonal stable isotope analysis on two types of tissue (muscle and liver). Isotope values were also obtained for zooplankton, whitefish larvae and eggs. We calculated the contribution of potential food sources for sticklebacks’ diet using a Bayesian mixing model (SIMMR). Furthermore, we determined stickleback trophic position, and δ15N and δ13C values were compared with those of other fish species of Lake Constance. The results of the Bayesian model as well as the stomach content analysis showed clear evidence of stickleback predation on fish eggs and larvae. Stickleback δ15N values were elevated during winter and comparable to those of piscivorous pike, while δ15N values of zooplankton were reduced, and those of whitefish larvae were similar to those of sticklebacks after accounting trophic fractionation of N isotopes. Trophic position calculations further identified sticklebacks as piscivorous, while the δ13C values of the liver and stomach content analysis suggests that a benthic-pelagic species pair may exist in Lake Constance. These findings support the hypotheses that sticklebacks in Lake Constance can display piscivorous feeding behaviour on sympatric fish species, most likely whitefish larvae and eggs.

Growth patterns and feeding characteristics in early developmental stages of Takifugu rubripes cultured in a recirculating aquaculture system

The growth patterns and feeding characteristics of Takifugu rubripes at different developmental stages (0–50 days after hatching, DAH) were investigated under artificial breeding conditions using ecological and traditional biological methods. The results revealed rapid growth in head length, head height, and eye diameter from hatching to 50 DAH, and the inflection point for body length growth occurred at 27 DAH. From 27 to 50 DAH, the growth rate slowed. In the swimming organs, the inflection points for tail, pectoral, dorsal, and anal fin growth occurred from 29 to 31 DAH. The growth rate for fins slowed after this period, suggesting the preferential development of important organs related to sensation, locomotion, and feeding during early development, with varied developmental periods. An investigation of the feeding rhythm of T. rubripes larvae, juveniles, and young fish showed that feeding activities mainly occurred during the daytime, a behavior typical of daytime feeders. The average daily feeding rate of T. rubripes was 12.61% for the early-stage larvae at 6 DAH, 43.89% for the late-stage larvae at 15 DAH, 40.05% for juveniles at 30 DAH, and 28.46% for young fish at 46 DAH. In addition, the satiation time for juveniles tended to decrease with increasing age, whereas the time for digestion tended to increase. These data can be used as a reference for the daily feeding of T. rubripes at different developmental stages. Comprehensive understanding of the growth and feeding characteristics of early-stage T. rubripes developed in this study will be useful for the management of artificially bred fry and will aid in promoting the growth and survival rates of aquaculture fish larvae.

The RNA-binding protein Adad1 is necessary for germ cell maintenance and meiosis in zebrafish.

The double stranded RNA binding protein Adad1 (adenosine deaminase domain containing 1) is a member of the adenosine deaminase acting on RNAs (Adar) protein family with germ cell-specific expression. In mice, Adad1 is necessary for sperm differentiation, however its function outside of mammals has not been investigated. Here, through an N-ethyl-N-nitrosourea (ENU) based forward genetic screen, we identified an adad1 mutant zebrafish line that develops as sterile males. Further histological examination revealed complete lack of germ cells in adult mutant fish, however germ cells populated the gonad, proliferated, and entered meiosis in larval and juvenile fish. Although meiosis was initiated in adad1 mutant testes, the spermatocytes failed to progress beyond the zygotene stage. Thus, Adad1 is essential for meiosis and germline maintenance in zebrafish. We tested if spermatogonial stem cells were affected using nanos2 RNA FISH and a label retaining cell (LRC) assay, and found that the mutant testes had fewer LRCs and nanos2-expressing cells compared to wild-type siblings, suggesting that failure to maintain the spermatogonial stem cells resulted in germ cell loss by adulthood. To identify potential molecular processes regulated by Adad1, we sequenced bulk mRNA from mutants and wild-type testes and found mis-regulation of genes involved in RNA stability and modification, pointing to a potential broader role in post-transcriptional regulation. Our findings suggest that the RNA regulatory protein Adad1 is required for fertility through regulation of spermatogonial stem cell maintenance in zebrafish.

Regulation of survival, growth performance, and intestinal health of large yellow croaker (Larimichthys crocea) larvae by sodium decanoate supplementation

A 30-day feeding trial was undertaken to elucidate the impact of diets supplemented with sodium decanoate (Sd) on survival, growth performance, and intestinal health in Larimichthys crocea larvae. A series of experimental diets consisting of graduated levels of Sd were formulated, including 0.0% (the control), 0.1%, 0.2%, 0.4%, or 0.8%. The study revealed no significant variations in survival among dietary groups. The growth performance (final body weight and specific growth rate) exhibited significant linear and quadratic trends, with the highest values observed in larvae fed a diet containing 0.2% Sd, which was significantly higher than that of the control group. Notably, Larvae fed diets with 0.2%–0.8% Sd had significantly higher intestinal fold height than the control group. A finding that was substantiated by the increased mRNA expression of pcna and odc, which are known to reflect processes of epithelial proliferation and differentiation. Meanwhile, the significant increase in the activity of the intestinal brush border membrane enzyme (Leucine-aminopeptidase), observed in diets supplemented with 0.1%–0.8% Sd, provides compelling evidence supporting the promotion of intestinal development and maturation. In terms of digestive and absorptive capacity, dietary supplementation with 0.4% Sd significantly increased the activity of trypsin and creatine kinase, while 0.1%–0.4% Sd specifically enhanced the activity of Na+-K+-Adenosinetriphosphatase than the control group. Importantly, larvae consuming Sd-supplemented diets at appropriate levels exhibited increased mRNA expression of tight junction-associated genes. Additionally, diets supplemented appropriate Sd improved the antioxidant capacity by modulating antioxidant enzymes and genes, antioxidant substances, and lipid peroxidation products. In summary, the diet incorporating 0.2% Sd could potentially boost the growth of larvae, which may be connected to Sd promoting intestinal health by regulating intestinal morphology and development, digestion and absorption capacity, intestinal barrier function, and antioxidant capacity. This study sheds light into the application of medium-chain fatty acids in marine fish larvae and contributes to the development of nutritional regulation strategies aimed at enhancing larval development.

Influence of extreme cold and warm oceanographic events on larval fish assemblages in the southern region of the California Current

The larval fish community in the southern region of the California Current (CC) was analyzed to test the hypothesis of a northward expansion of tropical species for the summer-fall seasons of La Niña (LN) 2010-2011, The Blob 2014, and El Niño (EN) 2015-2016. Interannual temperature anomalies (-5 to +2°C), as well as decreases in chlorophyll a (68%) and zooplankton density (71%), resulted in dramatic changes in the larval fish community, such as an 82% decline in larval fish density, unprecedented for the CC. Tropical species richness increased in the north by 46%, while temperate species decreased by 65% in the south. Mesopelagic species richness and relative abundance increased in the north by 53 and 92%, respectively. In the south, the species richness of the demersal component increased up to 39%, although demersal species were co-dominant with mesopelagic species, accounting for 47% of the relative abundance compared to 49% for the mesopelagic species. The magnitude of the changes in the community was unparalleled when compared with other warming events, such as EN 1983-1984 or EN 1997-1998. The differences were probably related to the presence of The Blob, which favored the transport of oceanic species into the neritic region of the CC. In both cold and warm years, fronts and mesoscale eddies in the middle part of the Baja California Peninsula represented barriers to the latitudinal distribution of species, even during intense tropicalization processes, since no latitudinal extensions in species distribution occurred.

Changes in digestive enzyme activities during the early ontogeny of milkfish, Chanos chanos larvae.

Knowledge of the developmental ontogeny of the digestive system and nutritional requirements of marine fish larvae is a primary requisite for their successful rearing under an optimal feeding regime. In this context, we assessed the activity profile of key digestive enzymes viz., trypsin, chymotrypsin, leucine aminopeptidase, lipase, amylase, and alkaline phosphatase during the early ontogeny of milkfish, Chanos chanos (0 day, 3 days, 6 days, 9 days, 12 days, 15 days, 18 days, 21 days, 25 days, and 30 days post-hatch). Larvae for this study were obtained from the successful breeding of milkfish at ICAR-Central Institute of Brackishwater Aquaculture, India. Growth curves (length and weight) of the larvae indicated a positive morphological development under a standardized feeding regime that comprised Chlorella salina, Brachionus plicatilis, Artemia salina nauplii, and commercial weaning feed for different larval stages. With respect to protein digestion, the specific activity of pancreatic enzymes trypsin and chymotrypsin and intestinal brush border leucine aminopeptidase showed two peaks at 3 dph and 15 dph, following the introduction of rotifer and Artemia nauplii. Similar bimodal peaks were observed for alkaline phosphatase and amylase activities, with the first peak at 3 dph and the second peak at 18 dph and 21 dph, respectively. Whereas in the case of lipase, high activity levels were observed at 0 dph, 3 dph, and 18 dph, with subsequent decreases and fluctuations. Overall, as most of the enzymes were found to have peak activities at 15 to 21 dph, this period can be potentially considered as the developmental window for weaning larvae from live to formulated feeds in milkfish hatcheries.

Effects of anthropogenic noise and natural soundscape on larval fish behavior in four estuarine species.

The larval and post-larval forms of many marine organisms, such as oysters, crabs, lobster, coral, and fish, utilize ambient acoustic cues to orient, settle, or metamorphose. In this study, the effect of anthropogenic and ambient sounds on the orientation behavior of four larval estuarine fishes was examined in a controlled, laboratory experiment. Pre-settlement size red drum Sciaenops ocellatus, southern flounder Paralichthys lethostigma, spotted seatrout Cynoscion nebulosus, and Florida blenny Chasmodes saburrae larvae were exposed to four sound treatments-control, estuarine soundscape, seismic airguns, and large-ship passage-in a linear acoustic chamber. Initial significant (p < 0.05) avoidance of airguns was observed in three of the four species (all but the Florida blenny), but habituation to this sound occurred as the experiment progressed. All species avoided ship passage sounds; however, the avoidance behavior was not significant. Interestingly, none of the species studied were significantly attracted to the acoustic cues alone of the estuarine soundscape; in fact, three of the four species spent less time near the speaker when it was broadcast. These results suggest that larval fish can potentially habituate to anthropogenic noise relatively quickly (<10 min). Understanding how sounds affect larval behavior is necessary because successful recruitment ultimately affects a population's success.

Effect of water temperature of culture medium on the sex ratio and survival rate of fighting fish Betta dennisyongi larvae

Fighting fish Betta dennisyongi is a popular ornamental freshwater fish in Indonesia. Male fighting fish are preferred because the colour pattern and shape of the fins are more attractive so they are more expensive. This study aims to determine the optimum temperature of rearing media water on the male sex ratio and survival rate of fighting fish larvae. A completely randomized design method with three replications was used in this study. The tested rearing temperature water was: 26°C, 28°C, 30°C, and 32°C. Fish were kept for 40 days. The results of the ANOVA test showed that larval rearing temperature affected significantly the ratio of male and female fish larvae survival (P<0.05). The highest percentage of the male sex was found at a temperature of 32 °C (93.33%), this value was significantly different from other temperature treatments. Meanwhile, the highest larval survival was obtained at a rearing temperature of 28 °C (80.00%), where this value was significantly different from other treatments. Therefore, with economic considerations, it is concluded that the optimal larval rearing media temperature is 28 °C.

The Effect of Difference Dose Quail Manure Fertilizer on The Population Growth of Daphnia sp. that Cultured in Soy Stew Water

Daphnia sp. is one of the alternative food organisms that potential to be developed on the availability of live food organisms in the hatchery cause has many benefits, like as easy to digest by fish larvae and being able to culture in massal. The study aims to know the effect of the different doses of quail manure on the growth pattern of Daphnia sp. that be cultured in soy stew water and to know the best dose of quail manure to increase the growth rate of Daphnia sp. The experimental method was employed in this research with a Completely Randomized Design (CRD) consisting of four treatments and four replicates. The treatments tested were the different doses of quail manure organic, that is 0 g/L, 2.5 g/L, 3 g/L, and 3.5 g/L. Daphnia sp. is cultured in a 10L jar with a media volume of 5L. Observation and calculations were carried out for 16 days with the initial density of Daphnia sp. being 30 indv/L. This research result showed that different doses of quail manure had a significant effect (P<0,05) on the growth pattern of Daphnia sp. The time value of the adaptation phase and the specific growth rate in treatment with a dose of 2.5; 3; and 3.5 g/L were not significantly different but better than treatment with a dose of 0 g/L, each of which is 0.243/day, 0.315/day, 0.322/day, and 0.310/day. The maximum density of each treatment was significantly different with the best value obtained at a dose of 3 g/L which was 1725 ind/L and the lowest was obtained at a dose of 0 g/L, which was 475 ind/L. Based on the result of this research, it can be concluded the treatment with a dose of 3 g/L of quail manure was the dose that gave the best growth for Daphnia sp.

Evaluation of yellow pumpkin seed extract (Cucurbita moschata D) on the successful masculinization of betta fish (Betta splendens)

Betta fish is one of the most popular freshwater ornamental fish. This ornamental fish is very popular among people of various ages because it is easy to maintain. However, fans of these ornamental fish prefer male fish over females because male fish have aesthetic values and better and attractive colors and have higher profits. The experiment aims to determine the effect of yellow pumpkin seed extract on the successful of male betta fish larvae, as well as giving the best dose. The design used was a completely randomized design (CRD) with 4 treatments and 3 replications. The immersion doses used were control A, treatment B with a dose of 40 mg/L, treatment C with a dose of 80 mg/L and treatment D with a dose of 120 mg/L. Maintenance period for 30 days. The results showed that soaking using yellow pumpkin seed extract with different concentrations had a very significant effect on the percentage of males. The percentage of male betta fish ranged from 40.00–90.00%, the percentage of female betta fish ranged from 5.00–45.00%, and the percentage of intersex betta fish ranged from 5.00–15.00%. The best concentration of yellow pumpkin seed extract was 120 mg/L with the percentage of male betta fish 90.00% in treatment D.Keywords: Betta splendens Larvae; Immersion; Maleization; Pumpkin Seed Extract

The Effect of Immersion Duration of java barb larvae (Barbornymus gonionotus) in the combination of thyroxine hormone and recombinant growth hormone (rGH) on the egg yolk absorption and growth

Java barb (Tawes) is one of the endemic freshwater fish in Indonesia which has being widely cultivated. The time rearing of Java barb from larva to market size is generally 5-6 months. Egg yolk absorption rate and growth of Java barb fish can be increased by hormonal manipulation using thyroxine hormone and recombinant growth hormone (rGH). The length of immersion time affects the performance of hormones in the fish’s body. The purpose of this study is to determine the effect of immersion duration and the best immersion time in a combination of thyroxine and rGH on the egg yolk absorption and the growth of Java barb larvae. This research was conducted on 23 August-1 November 2021 at Laboratorium Pengujian Kesehatan Ikan dan Lingkungan (LPKIL) in Muntilan, Magelang regency. The testing fishes used were early hatched Java barb fish larvae that still had egg yolks. The method used was a completely random design (CRD) with 4 treatments and 3 replications and each was done with a combination of 0.1 mg/l thyroxine hormone and 2.5 mg/l rGH with treatments A (control), B (1 hour immersion time), C (2 hours immersion time) and D (3 hours immersion time). The results showed that the effect of immersion duration in combination of thyroxine and rGH had a significant effect on the rate of egg yolk absorption and the growth of Java barb fish larvae. The best immersion time was treatment D (3 hours immersion duration) which resulted in 4%/hour of the absorption rate of egg yolk absorption rate, 12.53±0.15 mm absolute length growth, 0.047±0.002 g absolute weight growth, 13.82±0.15 % of specific growth rate, and 54.67±4.62 % survival rate.

Physiological responses of mechanosensory systems in the head of larval zebrafish (Danio rerio).

The lateral line system of zebrafish consists of the anterior lateral line, with neuromasts distributed on the head, and the posterior lateral line, with neuromasts distributed on the trunk. The sensory afferent neurons are contained in the anterior and posterior lateral line ganglia, respectively. So far, the vast majority of physiological and developmental studies have focused on the posterior lateral line. However, studies that focus on the anterior lateral line, especially on its physiology, are very rare. The anterior lateral line involves different neuromast patterning processes, specific distribution of synapses, and a unique role in behavior. Here, we report our observations regarding the development of the lateral line and analyze the physiological responses of the anterior lateral line to mechanical and water jet stimuli. Sensing in the fish head may be crucial to avoid obstacles, catch prey, and orient in water current, especially in the absence of visual cues. Alongside the lateral line, the trigeminal system, with its fine nerve endings innervating the skin, could contribute to perceiving mechanosensory stimulation. Therefore, we compare the physiological responses of the lateral line afferent neurons to responses of trigeminal neurons and responsiveness of auditory neurons. We show that anterior lateral line neurons are tuned to the velocity of mechanosensory ramp stimulation, while trigeminal neurons either only respond to mechanical step stimuli or fast ramp and step stimuli. Auditory neurons did not respond to mechanical or water jet stimuli. These results may prove to be essential in designing underwater robots and artificial lateral lines, with respect to the spectra of stimuli that the different mechanosensory systems in the larval head are tuned to, and underline the importance and functionality of the anterior lateral line system in the larval fish head.

Prevalence of Anisakis larvae in cultured mackerel Scomber japonicas in Japan and the relationship between the intensity of Anisakis infection in cultured mackerel and fish fatness

Incidences of food poisoning caused by Anisakis have increased in Japan, and a significant number of anisakiasis cases in Tokyo attributed to the consumption of mackerel (Scomber japonicus) have been reported. There are two types of cultured mackerel in Japan: those cultured fully from controlled parent fish eggs and those cultured from wild juveniles collected from the sea. In this study, we aimed to investigate the prevalence of Anisakis larvae in cultured mackerel (184 fish) in 15 products and identified the species using molecular analysis to evaluate the risk of food poisoning. In total, 1567 Anisakis larvae were detected in 70 of 130 mackerel in 10 products; however, Anisakis larvae were not detected in 54 mackerel using artificially reared juveniles in 5 products. Moreover, 277 larvae were detected in fish muscle, and 98.6 % (273/277 larvae) were molecularly identified as Anisakis simplex sensu stricto (A. simplex). Conversely, 1043 Anisakis pegreffii larvae were identified genetically and/or morphologically but only 2 larvae were identified in the muscle. There was no significant relationship between the host coefficient of fatness and the infection intensity of Anisakis larvae in individual fish (Spearman's rank correlation coefficient test, P > 0.05). Based on the results of the analysis of the cytochrome c oxidase subunit2 (cox2) gene of A. simplex and A. pegreffii detected in this study, we attempted to estimate the catch area of the juveniles (Pacific stock and Tsushima Warm Current stock). The clusters on the phylogenetic tree of the cox2 gene of A. pegreffii from the mackerel presumed to be the two above mentioned geographic distributions were not separated and these geographic origins could not be estimated. This study revealed that mackerel cultured using wild juveniles are likely to be contaminated with Anisakis larvae, which can be detected not only in the visceral organs, but also in the muscle. Anisakis infection in cultured mackerel did not influence fish growth and evaluating the intensity of Anisakis based on the fatness level of the mackerel was complicated. To prevent anisakiasis caused by the consumption of mackerel cultured using wild juveniles, it is important to steadily control Anisakis through heating and freezing.